Soft contact lenses can generally be classified into two groups: conventional hydrogel contact lenses and silicone hydrogel contact lenses. Conventional hydrogel lenses are typically formed from hydrophilic polymers and copolymers such as those containing repeating units from hydroxyethylmethylacrylate (“HEMA”) and methacrylic acid (“MAA”). Contact lenses formed from copolymers of HEMA and MAA, such as ACUVUE® 2™ contact lenses, display substantial amounts of lysozyme uptake. See, e.g., Castillo et al, Biomaterials v 6(5), pp 338-345 (1985) It is believed that the anionic charge of the MAA drives the high adsorption of the cation, a natural protein that exhibits anti-bacterial properties. See, e.g., Ibrhahim et al., J. Agric Food Chem., v 39, pp 2077-2082 (1991). However, one of the biggest drawbacks of conventional hydrogel contact lenses is that they generally have relatively low oxygen permeability.
Silicone hydrogel contact lenses offer an advantage over conventional hydrogel contact lenses in that they improve oxygen permeability, which improves oxygen availability to the cornea. However, silicone monomers are typically not anionic, and thus, do not display substantial amounts of lysozyme uptake. Thus, it would be desirable to add anionic groups to a silicone hydrogel to aid in the adsorption of native lysozyme.
2-Acrylamido-2-methylpropane sulfonic acid (“AMPS”) is an anionic monomer that has been incorporated into conventional hydrogel lenses. See, e.g., U.S. Pat. Nos. 5,451,617 and 5,011,275 and US Patent Application No. 2008/0114123. However, Applicants found that upon attempting to incorporate this anionic monomer into a silicone hydrogel, the monomer was not very soluble and resulted in a hazy mixture. The present invention relates to the discovery of a method of incorporating AMPS or other sulfonic acid-containing components in a silicone polymer/hydrogel, which in turn can be used to manufacture silicone hydrogel contact lens having anionic properties and the benefits therefrom.